The development of the next generation of wireless mobile communications for 5G cellular communication is underway. With spectrum always being at a premium, engineers are turning to millimeter wave frequencies to provide those next generation services. Millimeter wave frequencies are found at 30 to 300 GHz. There is also considerable interest in using frequencies from and above 28 GHz.
However, while the above spectrum is presently unused for LTE as licensed spectrum such that it could be used to realise multi-gigabit wireless communication, it is well-known within the art that electromagnetic waves at these frequencies suffer from high attenuation and high path loss, which, consequently, limits the cell sizes that can be realised.
Various techniques exist for addressing path loss, which include using a diversity technique, such as, for example, spatial diversity/multiplexing, in which two or more different transmit signals are used to increase overall throughput, and beam forming, in which two or more instances of the same signal are used to improve communication reliability.
Nevertheless, millimeter waves present several beam forming technical challenges that comprise, firstly, delay spread and angular spread, which are particularly problematical under Non-Line Of Sight (NLOS) conditions such as found indoors, and, secondly, beam misalignment, which arises when channel state information or beam tracking is inaccurate due to, for example, at least one or more of measurement errors and user equipment mobility.